1. Field of the Invention
The present invention is related to mechanical fastening devices, in particular those used for connecting a wide variety of rigid or flexible materials.
2. Prior Art
Devices which interconnect two surfaces by use of interdigitated parts are known. Also known are devices which effect a connection by means of a doubly tapered wedge inserted into a similarly shaped aperture.
Slide fasteners, hook and loop devices, other press together systems, and various forms of interlocking longitudinal shapes such as those used in plastic food storage bags are commonly utilized for attaching flexible materials. Certain of these devices may provide for lineal adjustability. Rigid materials are sometimes connected by interdigitated mortises and tennons and various types of interlocking joints, such as the dovetail joint common to woodworking.
In regard to fastening flexible materials such as apparel, fabric, leather, rubber, plastics, or other flexible sheet goods the zipper is probably the most common means in use today. The zipper has considerable merit as a quick, relatively secure fastening device which can be readily detached, but it also has several disadvantages. The minimal surface area which actually acts against tensile forces can be over stressed causing failure. Extraneous materials such as hair or nearby fabric can readily jamb the fastener. Once jammed or broken the zipper is often rendered dysfunctional over its entire length and usually must be wholly replaced. The necessity of a sliding connector and its gripping device adds bulk and directionality to the overall unit which can be a negative aesthetic or functional consideration in many applications. It is not self-concealing thereby normally necessitating a covering flap or hem. The zipper requires directional attachment starting only at a connected end. A degree of manual dexterity is required which may be a disadvantage for people with certain disabilities as well as for those wearing gloves. For most applications it can not readily be made of plastic or other inexpensive low strength materials, and a highly precise capital intensive manufacturing system is necessary.
Hook and loop systems such as those produced under the tradename VELCRO, generally emanating from U.S. Pat. No. 2,717,437 to Mestral, are another common fastening method with considerable utility which are commonly used to connect flexible materials. Hook and loop systems also have several significant disadvantages. The force necessary to effect disengagement is directly related to the strength of the connection thereby limiting potential strength and at the same time requiring excessive force to effect disconnection. Precise register of the connection is difficult to achieve. The device is essentially designed to resist uplifting stresses although it is most commonly employed to resist stresses normal to the connected surfaces. Unintended foreign materials are easily attracted. Cleaning is difficult. Repetitive washing and/or use tends to weaken the connecting fibers. Strength is at least in part related to the profile thickness thereby frequently resulting in a bulky appearance. The texture of the exposed surface may cause discomfort or skin irritation. Specialized manufacturing methods are required and material choices are limited. In addition to the above, many people find both the exposed texture and the sound of disengagement to be objectionable.
Other systems of interconnecting shapes have also been developed and improved such as interlocking hermaphroditic "mushroom"-like projections, as per U.S. Pat. No. 3,192,589 to Pearson, which are pressed into each other so that the head of one such member is contained within the complementary heads and stems of a plurality of its counterparts. Vertical detachment is resisted by partial contact of the opposing under-surfaces. The base and/or the projection must be of sufficient resilience to allow insertion and removal. A recent example is U.S. Pat. No. 5,625,929 to Hattori which recognizes the inherent problem of such systems in resistance to horizontal shear and presents a means of limiting lateral slippage in a mushroom type fastener by providing a geometric pattern to the projections. These devices generally share many of the same disadvantages as hook and loop connectors, as stated above, in particular the direct relationship of strength to the force necessary for disconnection.
Several devices are presented in U.S. Pat. No. 5,269,776 to Lancaster and Young, for the purpose of fastening a disposable diaper, which utilizes a system of arrayed digits and apertures. Although it appears that this device will resist lateral stress via shear along the adjacent surfaces it is apparent that the digits of such a system will also tend to deform and release when a certain level of stress is applied. Again, the lateral stress resistance is related to the available release force. A similar concept is presented in U.S. Pat. No. 5,447,772 to Flieger.
It can be seen that a common characteristic of most of these "press together" devices is that they are primarily dependent on the tensile strength of the connecting elements to resist stresses both perpendicular and normal to the surface, more or less equally. Therefore, when sheared laterally, i.e. normal to the surface, the engaged elements tend to bend and align axially toward the direction of stress until failure is initiated by the release of a single connecting set. Since they are designed to primarily resist vertical tensile stresses, such devices are inherently limited in strength by the force necessary to voluntarily disengage the connection. Therefore, resistance to lateral stress, necessary release force, and failure stress are inherently related, a characteristic that can only be compensated for by substantially increasing the area of contact and actuating release by a peeling motion. Hook and loop systems, mushroom, and similar devices also generally tend to require a thickness which is at least partly proportional to strength. Therefore, a fastener offering reasonable strength generally must be relatively thick in profile: an aesthetic or functional disadvantage in many applications.
It will be recognized that in many, perhaps most, common applications of these devices horizontal shear stress on the assembly is predominant--not vertical tension. This is true, for instance, where such a device is used to close a shoe or jacket, in belt or band applications, or wherever the primary stress on a joint is normal to the surfaces to be connected. Therefore, in such applications, the integrity of the connection is typically limited by the necessity to provide relatively easy detachment--and the force necessary to achieve detachment is typically greater than that warranted for the use. Such systems are not inherently resistant to shear stresses and generally tend to deform and weaken rather than form a tighter bond when such stresses are applied.
Several other existent devices allow for lineal adjustment between overlapping surfaces. U. S. Pat. No. 3,484,907 to Elsenheimer describes several methods of effecting an adjustable fastener, one embodiment of which utilizes offset pairs of male/female shapes which are dovetail in profile and rectangular in plan. In this case lateral resistance is effected by the stop at the end of a slotted chamber and adjustment is effected by bypassing one surface to another set of male and female connectors. More recently U.S. Pat. No. 5,640,744 and others to Allan disclose adjustable straps utilizing interdigitated sloped links or teeth within a track which appears to be reasonably resistant to one-directional shear stress.
Numerous types of single point fasteners have been developed over time, the most common of which is the button. Other devices such as the snap fastener, various forms of buckles and hook and eye systems generally tend to have limitations as to their utility. Buttons and buckles are generally highly visible. Most of these systems provide one dimensional connection but allow lateral rotation. Though generally proven useful for particular applications each tends to have certain disadvantages which may limit utility. U.S. Pat. No. 78,116 to Moore describes a two piece "button" which interconnects by means of a compound dovetail and wedge and also includes a latching mechanism. By wedging the male structure into a receiving shape a fixed connection is effected which appears to resist shear. However, the male and female parts are not interchangeable, the male member has no base to provide rigidity, the device tends to rotate vertically when stressed, and the invention generally suffers from an attempt to appear like a common button. It appears to have little or no advantage over snap-type fasteners later developed.
Continuous interlocking spline joint systems, as for instance those commonly used for plastic food storage bags are useful for many applications, but also have certain disadvantages. Precise alignment and manual dexterity are required to obtain closure. Opening and reuse can be problematic. It is generally difficult to ascertain whether a seal has been effected. Strength is limited, applications are limited, and material and manufacturing methods are limited.
In regard to connecting rigid or semi rigid materials such as wood, sheet or structural metals, plastics, stone, etc. several methods exist which utilize interdigitated or singular oblique meeting surfaces. The "dovetail joint", for instance, is commonly used in woodworking and has sometimes been adopted for use with other materials. Typically the interdigitated dovetail is used as a method for permanently attaching planar materials at a right angle. By interconnecting a series of like shapes which are wider at one extremity than the other an effective joint is created which resists considerable stress. This type of joint is normally incised through the thickness of each joining member and must be used in conjunction with an adhesive on the contacting surfaces or some type of mechanical locking device in order to resist detachment. In a planar condition a dovetail connection with open faces would tend to slide apart unless fixed in place by other means. Several U.S. Patents have been issued for various improvements to such devices such as U.S. Pat. No. 435,759 to Marter but all appear to be related to a right angle connection, and generally employ unequal parts.
Singular sets of tapered dovetail and wedge connectors have been utilized for a several devices. U.S. Pat. No. 3,050,124 to Ottenbacher describes a pitless well adapter in which a waterproof joint is effected by gravitational pressure applied to such a device. U.S. Pat. No. 4,019,298 to Johnson utilizes a similar mechanism to effect a beam suspension system, also dependent on gravity, as well as a means of maintaining engagement utilizing a linear detent and corespondent depression on the sloped sides of the dovetail. More recently, U.S. Pat. No. 5,425,524 to Messina describes a leveling and guiding device for hanging objects which includes triangular members having a "dovetail" profile. In these and several other previously patented devices a connection is described between two unlike parts, male and female, typically singular sets dependent on gravity, which are utilized to effect a fixed structural condition. In general, such devices have been designed to align and/or join two specific male and female parts and are neither presented nor claimed as a generic multipurpose interlocking device. None are proposed for use in a plural or hermaphroditic configuration and none provide multi-directional fastening capabilities.
Various devices have been utilized to provide an electrical connector, generally including a plurality of male pins inserted into a plurality of female receptacles. Generally these devices are prone to disconnection when tension is applied and the pins are often subject to mechanical damage.
It can be seen from the foregoing that, based of the numerous systems presently available, there is a need for an interlocking device which provides simplicity, functional strength unrelated to the force necessary for disconnection, means of maintaining engagement, self alignment, minimal visibility, ease of manufacture, multiplicity of function, and diverse other advantages.